A Wi-Fi network may be formed by one or more access points (APs) that provide a wireless communication channel or link with a number of client devices or stations (STAs). Each AP, which may correspond to a Basic Service Set (BSS), periodically broadcasts beacon frames to enable any STAs within wireless range of the AP to establish and/or maintain a communication link with the Wi-Fi network. The beacon frames, which may include a traffic indication map (TIM) indicating whether the AP has queued downlink data for the STAs, are typically broadcast according to a target beacon transmission time (TBTT) schedule.
In a typical Wi-Fi network, only one device may use a shared wireless medium at any given time. To arbitrate access to the shared wireless medium, the IEEE 802.11 standards define a distributed coordination function (DCF) that instructs individual STAs (and APs) to “listen” to the medium to determine when the medium is idle (e.g., using a “carrier sense” technique). When a STA detects that the wireless medium has been continuously idle for a DCF Interframe Space (DIFS) duration, the STA may attempt to transmit data on the wireless medium. Many Wi-Fi networks operating in the 5 GHz frequency band employ an Enhanced Distributed Channel Access (EDCA) mechanism for medium access contention operations. The EDCA mechanism is an example of a listen-before-talk (LBT) protocol.
For example, to prevent multiple devices from accessing the wireless medium at the same time, each device may select a random “back-off” number or period. At the end of the DIFS duration, a contention period begins during which each device waits for a period of time determined by its back-off number (e.g., its back-off period) before it attempts to transmit data on the wireless medium. The device that selects the lowest back-off number will have the shortest back-off period (e.g., the earliest slot time in the contention period), and therefore “wins” the medium access contention operation. If multiple devices select the same back-off value and then attempt to transmit data at the same time, a collision occurs and the devices contend for medium access again using an exponential back-off procedure in which each device doubles the value of its back-off number for each subsequent medium access contention operation.
Other wireless networks may operate on the 5 GHz frequency band, and thus may share the same wireless medium with an IEEE 802.11-compliant wireless network. These other wireless networks may not employ an exponential back-off procedure for collision avoidance, and therefore devices associated with these other wireless networks may have an advantage over devices associated with EDCA-based wireless networks when contending for medium access. For example, channel access mechanisms associated with the European Telecommunications Standards Institute (ETSI) Broadband Access Network (BRAN) for Load Based Equipment (LBE) may not employ exponential back-off procedures for collision avoidance, which in turn may give wireless devices operating according to LBE protocols an unfair advantage over wireless devices that employ EDCA mechanisms for collision avoidance.
Thus, would be desirable for LBE-based devices and EDCA-based devices to more fairly contend for access to a shared wireless medium.